Optical fiber-based gamma calorimeter (OFBGC)

Abstract

An optical fiber-based gamma-ray calorimeter (OFBGC) sensor array which uses a thermal mass with a low thermal conductivity is provided. Advantages of the OFBGC sensor array include: 1) the number of sensors in the OFBGC sensor array is adjustable and limited only by the spatial resolution of the OFBGC sensors, within the OFBGC sensor array, and 2) the OFBGC sensor design is simpler to build than a conventional optical fiber-based gamma thermometer (OFBGT) sensor array. One purpose of the OFBGC is to determine the power distribution in nuclear reactors.

What is claimed: 
     
       1. An optical fiber-based gamma calorimeter (OFBGC) comprising:
 a thermal mass; 
 an insulating tube disposed within a central region of the thermal mass; 
 a plurality of optical fiber sensors running through respective holes in the insulating tube, wherein the optical fiber sensors are configured to monitor a temperature of the thermal mass; 
 an outer sheath; 
 a gas backfilling between the thermal mass and the outer sheath; and 
 a heating wire running through two holes in the insulating tube, 
 wherein the heating wire has a predetermined length and linear heating rate, q′(z), and 
 wherein the linear heating rate q′(z), is used to derive a relationship with an axially dependent temperature difference, ΔT(z), between the plurality of optical fiber sensors to calibrate the OFBGC. 
 
     
     
       2. The OFBGC of  claim 1 , wherein the heating wire comprises nichrome. 
     
     
       3. The OFBGC of  claim 1 , further comprising an additional optical fiber configured to monitor a temperature of the outer sheath. 
     
     
       4. The OFBGC of  claim 3 , wherein the additional fiber is disposed within a capillary tube connected to the outer sheath. 
     
     
       5. The OFBGC of  claim 1 , wherein the thermal mass comprises at least one of quartz or mullite. 
     
     
       6. The OFBGC of  claim 1 , wherein the number of sensors is adjustable. 
     
     
       7. The OFBGC of  claim 1 , wherein the thermal mass is a low-thermal conductivity annular cylindrical mass, and wherein the insulating tube and the annular cylindrical thermal mass are an integrated structure. 
     
     
       8. The OFBGC of  claim 1 , wherein the thermal mass is annular in shape. 
     
     
       9. The OFBGC of  claim 1 , wherein the insulating tube is at least one of a thermocouple wire insulator or a 4-hole tube that is an electrical insulator. 
     
     
       10. The OFBGC of  claim 1 , wherein the gas backfilling is an inert gas. 
     
     
       11. An optical fiber-based gamma-ray calorimeter (OFBGC) sensor array comprising:
 an optical fiber, 
 a heating wire, 
 wherein the optical fiber is used to measure the temperature of an annular cylindrical thermal mass with a low thermal conductivity, 
 wherein the heating wire has a predetermined length and linear heating rate, q′(z), and 
 wherein the linear heating rate q′(z), is used to derive a relationship with an axially dependent temperature difference, ΔT(z), between the optical fiber and a second optical fiber-based temperature sensor to calibrate the OFBGC. 
 
     
     
       12. The OFBGC sensor array of  claim 11 , wherein the annular cylindrical thermal mass is quartz glass or the annular cylindrical thermal mass has the geometrical form of a low-thermal conductivity circular cylindrical tube that extends the total axial length of the OFBGC sensor array. 
     
     
       13. The OFBGC sensor array of  claim 12 , wherein a hole within the tube has a diameter that is larger than the diameter of an optical fiber. 
     
     
       14. The OFBGC sensor array of  claim 12 , wherein the optical fiber runs the length of the tube and is configured to measure the temperature of the thermal mass. 
     
     
       15. The OFBGC sensor array of  claim 11 , wherein the thermal mass is centered within a thin-walled metallic outer sheath, and a gas gap fills the volume between the thermal mass and an outer sheath. 
     
     
       16. The OFBGC sensory array of  claim 15 , wherein the temperature of the outer sheath is measured with the second optical fiber-based temperature sensor that is attached to the outer surface of the outer sheath. 
     
     
       17. The OFBGC sensory array of  claim 16 , wherein a temperature difference is measured between the second optical fiber-based temperature sensor that is within the thermal mass and the optical fiber-based temperature sensor that is attached to the outside of the outer sheath. 
     
     
       18. The OFBGC sensor array of  claim 17 , wherein the temperature difference is measured for any axial position or any axial height within the OFBGC sensor array. 
     
     
       19. The OFBGC sensor array of  claim 11 , further comprising an adjustable number of sensors, wherein the number of sensors is limited by the spatial resolution of the sensing technique, or the spatial resolution of the sensors, within the OFBGC sensor array, based on thermal transport characteristics.